1. Field of the Invention
The present invention relates to an electromagnetic relay in which the connection of a signal transmission path is switched by controlling an electromagnet which rocks an armature.
2. Description of the Related Art
FIG. 1 is a cross-sectional view showing a conventional electromagnetic relay.
In the conventional electromagnetic relay 101, an electromagnet block 130 and a contact spring block 120 are contained within a case 140. An opening portion is provided at the lower portion of the case 140 and a relay board 110 is fitted into the opening portion.
The electromagnetic block 130 is provided with a spool 134 formed integrally with a core 131 and an insulating member. A coil 133 is wound in the groove of the spool 134. An electromagnet 138 thus constituted is provided in the electromagnetic block 130. The core 131 is generally U-shaped and the both end portions of the core 131 serve as magnetic poles 131a and 131b, respectively, of the electromagnet 138. A permanent magnet 132 is arranged almost at the central portion of the core 131.
The electromagnetic relay 101 is also provided with an armature 136 made of magnetic material. A protrusion-like support portion 136c polarized by the permanent magnet 132 is formed at the central portion of the armature 136. The armature 136 is rockable like a seesaw with respect to the electromagnet 138 about the support portion 136c. Studs 137a and 137b protruding in the opposite direction to the support portion 136c are provided on the tip ends of arms 136a and 136b of the armature 136, respectively. A hinge spring (not shown) applying an elastic force in the direction in which the end portion of the arm 136a is abutted against the magnetic pole 131a, is provided at the central portion of the armature 136.
The magnetic force of the electromagnet 138 is set higher than a combination of the recovery force of the hinge spring, the magnetic force of the permanent magnet 132 and the like. Thus, while the electromagnet 138 is de-excited, the end portion of the arm 136a of the armature 136 is abutted against the magnetic pole 131a by the recovery force of the hinge spring and the magnetic force of the permanent magnet 132. While the electromagnet 138 is excited, the end portion of the arm 136b is abutted against the magnetic pole 131b by the magnetic force of the electromagnet 138.
FIG. 2 is a plan view showing the contact spring block 120 of the conventional electromagnetic relay 101.
In the contact spring block 120 of the electromagnetic relay 101, a make contact plate spring 121 and an earth contact plate spring 123 serving as signal contact springs are connected to each other by a spring connection portion 150. A break contact plate spring 122 and an earth contact plate spring 123' serving as signal contact springs are connected to each other by a spring connection portion 150'. The spring connection portions 150 and 150' are the same in width as the respective contact plate springs. These plate springs are made of conductive members. A first movable spring part is constituted by the make contact plate spring 121, the earth contact plate spring 123 and the spring connection portion 150. A second movable spring part is constituted by the break contact plate spring 122, the earth contact plate spring 123' and the spring connection portion 150'. The make contact plate spring 121 and the break contact plate spring 122 are arranged to put a spring fixing part 124 therebetween. The spring fixing part 124 is fixed to the front surface of the relay board 110.
The direction in which the first and second movable spring parts extend is the same as the lengthwise direction of the armature 136.
The free end of the make contact plate spring 121 and that of the break contact plate spring 122 are T-shaped. Make contacts 121a and 121a' are provided on the free end portions of the make contact plate spring 121, respectively. Brake contacts 122a and 122a' are provided on the free end portions of the break contact plate spring 122, respectively. Earth contacts 123a and 123a' are provided on the end portions of the earth contact plate springs 123 and 123', respectively. The make contact 121a is provided at a position between the make contact 121a' and the earth contact 123a'. The break contact 122a is provided at a position between the break contact 122a' and the earth contact 123a.
FIG. 3 is a plan view showing the relay board 110 of the conventional electromagnetic relay 101.
Make contact terminals 111' and 111 are provided at such positions as to match with the make contacts 121a and 121a', on the relay board 110 of the electromagnetic relay 101, respectively. Brake contact terminals 112' and 112 are provided at such positions as to match with the break contacts 122a and 122a' on the relay board 110, respectively. Earth contact terminals 113 and 113' are provided at such positions as to match the earth contacts 123a and 123a' on the relay board 110 of the electromagnetic relay 101, respectively. A coil contact terminal 114 is provided at a position at which the earth contact terminal 113' is put between the coil contact terminal 114 and the make contact terminal 111'. A coil contact terminal 114' is provided at a position at which the earth contact terminal 113 is put between the coil contact terminal 114' and the break contact terminal 112'. These contact terminals are positioned on the lengthwise end portions of the relay board 110.
The make contact terminals 111 and 111' are provided with make fixed contacts 111a and 111a' formed on the front surface of the relay board 110 and make solder connection pads 111b and 111b' formed on the back surface of the board 110, respectively. The make fixed contacts 111a and 111a' are signal fixed contacts and the make solder connection pads 111b and 111b' are used to be mounted on an external mounting board (not shown). The break contact terminals 112 and 112' are provided with break fixed contacts 112a and 112a' formed on the front surface of the relay board 110 and break solder connection pads 112b and 112b' formed on the back surface thereof, respectively. The break fixed contacts 112a and 112a' are signal fixed contacts and the make solder connection pads 112b and 112b' are used to be mounted on the external mounting board.
The earth contact terminals 113 and 113' are provided with earth fixed contacts 113a and 113a' formed on the front surface of the relay board 110 and earth solder connection pads 113b and 113b' formed on the back surface thereof, respectively. The coil contact terminals 114 and 114' are provided with coil fixed contacts 114a and 114a' formed on the front surface of the relay board 110 and coil solder connection pads 114b and 114b' formed on the back surface thereof, respectively.
The make fixed contact 111a' of the make contact terminal 111' and the break fixed contact 112a' of the break contact terminal 112' are connected to each other. The fixed contacts and solder pads of the terminals are connected to one another by connection parts provided within the board, respectively, and the fixed contacts of the respective terminals serve as terminals of the signal transmission path. The earth fixed contacts 113a and 113a' of the earth contact terminals 113 and 113' are connected to an earth layer 115.
The make contacts 121a and 121a' of the make contact plate spring 121 are arranged to face the make fixed contact 111a' and 111a, respectively. The break contacts 122a and 122a' of the break contact plate spring 122 are arranged to face the break fixed contacts 112a' and 112a, respectively. The earth contacts 123a and 123a' of the earth contact plate springs 123 and 123' are arranged to face the earth fixed contacts 113a and 113a', respectively.
FIG. 4 is a plan view showing the positional relationship between the contact plate spring 120 and the armature 136 in the conventional electromagnetic relay.
In the conventional electromagnetic relay 101 thus constituted, the end portion of the arm 136a of the armature 136 is polarized by the magnetic pole 131a while the electromagnet 138 is de-excited. At this moment, the free end of the break contact plate spring 122 and that of the earth contact plate spring 123 fixed to the spring fixing part 124, are pressed by the stud 137b provided at the arm 136b of the armature 136.
The end portion of the arm 136b of the armature 136 is polarized by the magnetic pole 131b while the electromagnet 138 is excited. At this moment, the free end of the make contact plate spring 121 and that of the earth contact plate spring 123' fixed to the spring fixing part 124, are pressed by the stud 137a provided at the arm 136a of the armature 136.
In this way, the closing operations of the contacts 122a', 122a and 123a for the respective fixed contacts 112a, 112a' and 113a and those of the contacts 121a', 121a and 123a' for the respective fixed contacts 111a, 111a' and 113a' are conducted alternately. A desired connection state is then selected in the electromagnetic relay 101.
In the above-stated electromagnetic relay, however, while the break contacts 122a, 122a' and the earth contact 123a are connected to the fixed terminals 112', 112 and 113, respectively, for example, as shown in FIG. 4, the following Formula (1) is satisfied, where the distances between the center line parallel to the lengthwise direction of the armature 136 and the contacts 123a, 122a and 122a' are D21, D22, D22', respectively and contact pressing forces applied to the contacts 123a, 122a and 122a' are F21, F22 and F22', respectively: EQU F22.times.D22+F22'.times.D22'&gt;F21.times.D21 (1).
The contact pressing force is the repulsion of each of the pressed contact springs.
Due to this, while the contacts 123a, 122a and 122a' are connected to the fixed terminals 112', 112 and 113, respectively, a torque is generated about the center line parallel to the lengthwise direction of the armature 136 and the armature 136 is twisted. As a result, the seesaw operation of the armature 136 is inhibited to thereby disadvantageously adversely influence the closing/opening operation characteristics of the electromagnetic relay.
In the above-stated conventional electromagnetic relay, while the electromagnet 138 is de-excited, the contacts 122a and 122a' are closed by the fixed contacts 112a' and 112a and the break contact spring 122 becomes part of the transmission path. On the other hand, the earth contact 123a' of the earth contact spring 123' connected to the break contact spring 122 is not connected to anywhere and opened. Owing to this, if seen from the input terminal of the transmission path between the break contacts 122a and 122a', impedance of the earth contact spring 123' corresponds to being connected in parallel to the transmission path. As a result, input impedance is lowered and the high frequency characteristics of the transmission path deteriorates.